<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>可选链操作符</title>
</head>

<body>

    <script>
        //?.
        function main(config) {
            // const dbHost = config && config.db && config.db.host;
            //和上面一样的功能，逐个判断
            const dbHost = config?.db?.host;


            console.log(dbHost);


        }

        main({
            db: {
                host: '192.168.1.100',
                username: 'root'
            },
            cache: {
                host: '192.168.1.200',
                username: 'admin'
            },
        })



    </script>


</body>

</html>